It's Not My Problem
by Datura Writii
Summary: Marceline is visiting her twin in Aaa, where Prince Gumball is brooding over the Flame Prince endangering Fiona. Marshall Lee doesn't expect bringing his sister to the Candy Kingdom will result in something much more than cheering up the prince. Will Marshall Lee really tear off Prince Gumball's gumballs if he pursues Marceline? ...Eh. It's not my problem.
1. Let's Go to the Land of Aaa

**Author's Notes** | _It's Not My Problem is based on Adventure Time. I had a tough time trying to fit the gender-swapped episode in here without going against the facts the show in here, so please forgive any untrue little tidbits. Especially any dates. I just made up follows Marceline and Prince Gumball's relationship, with switching their third-person views. Sometimes I try to focus on Marcy's thoughts and sometimes Gumball's. There is also some Marshall Lee and Fiona, but not very much. Just mentions. Enjoy!_

**Poll Notice:**_I have a poll on my profile that lets you vote for what fanfiction you want me to continue/submit/start. Also feel free to PM me requests._

**Disclaimer**: I do not own Adventure Time or its characters, Frederator Studios does. I do, however, own the whole Ooo-Aaa setup with the relations between the gender-swapped characters. I didn't steal(or try to steal) any relations that other people thought up. Some of the details in here may not match the official show.

* * *

The Vampire Queen lounged on her plush bed, too put out to even float. Her ax bass lay dejectedly in the far corner of her room. Her diary sat on her bedside table, recently written in with deep black scratches that probably were bleeding into the opposite page as she sighed. And sighed. And sighed.

"Marceline!" Finn's voice.

"What?" The girl rolled off her bed, hitting the floor with a loud thump before slithering down her ladder and landing in the living room. Jake and Finn had their faces pressed against the glass of her porch door, cheeks comically squished outwards.

"We have mail for you," the friends said, voices muffled. Jake's orange arm wiggled into view like a limp piece of pasta, holding a black envelope with "Marceline" written on it in blunt red letters. She recognized the handwriting and grinned.

"Thank you," said Marceline as she cracked the door open, snatched the letter, and slammed the door shut, much to the two's disappointment. They sulked off with their heads low. She overheard them murmuring little insults like "no fun" and "Cloud Hunt's better" with her sensitive hearing, but didn't care.

"Marcy," she began to read aloud after Jake and Finn were out of earshot, "what's up?! It is high hell here on the other side of the earth. Gumballs is being no fun lately and Fiona is off with Cake to visit Ooo. Why don't you come over to Aaa for a bit? Not like you have anything to do!" Marceline paused, snorting and retorting to the paper, "Neither do you." She continued anyway, "Train ticket enclosed, my treat. See you soon, twinny. Hate, Marshall Lee Abadeer."

Marceline left her ax bass in the corner as she packed.

* * *

"Marshall Lee, you don't look a day over five hundred," said the Vampire Queen as she stepped off the candy train just after it grinded into the station, spitting out cotton candy clouds.

"Marceline, you old bat," Marceline's twin cackled as she tackled him and grinded her knuckles into his head.

"You're carrying my luggage," she chuckled before slinging the messenger bag around her shoulder into Marshall's arms.

"Glob, you sure packed a lot." The gray-skinned man groaned before fastening the bag over his neck.

"Unlike you, I actually wear something other than the same thing every day," Marceline stated matter-of-factly, picking at his red flannel.

"Don't dis the flannel," he said, hooking his arm with his twin's as they floated out of the station of Aaa. "So how's Daddy dearest?"

"Annoying as always. Luckily I don't have to talk to him much. Much. When's the last time you gave him a call, anyway? He's in the middle of the earth, we're equal distances away," she reminded him.

"We're not really on the best of terms. He always liked you better anyway," her twin responded.

"Whatever. Ah, it's been so long since I've been in Aaa," Marceline appreciated the kingdoms below as they approached Marshall Lee's cave.

"Three centuries."

"I don't count that. All I did was stay in your house and help you on that duet," the vampire snorted. "You better believe I'm going out and meeting all your friends and embarrassing you."

"About my friends…Like I said…Fiona and Cake are both visiting Finn and Jake."

"You don't have any other friends?" An eyebrow rose skeptically. She always did know her twin like the back of her hand. Probably because it had been introduced to his face on multiple occasions.

"Well, Gummy boy, but he's acting über odd lately."

"Yeah, Bubs has been, too. Ever since Finn started hanging out with Flame Princess."

"Ooo has a Flame Princess?" Marshall glanced over at Marceline with mild interest as they landed at his blue house's porch.

"Yeah, why?" Marceline let herself in as Marshall stood on his porch, face drawn up in thought.

"We have a Flame Prince. I wonder if…Fiona has been hanging out with him…"

"Does that make you jealous?" The Vampire King glanced up with a blush to see his twin's face upside-down and much closer than before, both fangs visible in her mischievous smile. "I know you've been crushing on her," she sang before Marshall batted her away.

"So has Glob balls, I think. Probably made him pink butt hurt." Marceline chuckled at her flustered counterpart. He'd always been the crude one, using nonsensical language and less than acceptable manners. At least Marceline had a grasp on lady-like etiquette. Marshall Lee was about as gentlemanly as Jake. Actually, Marshall made Jake look like Peppermint Butler.

"Anyway, where's your ax bass?"

"Left it at home," Marceline sighed, forlorn once again. "Can't write, sing, play, anything. I have awesome-block."

"Then maybe the break is necessary. Let's go eat some strawberries or crying children. I'm starved."

"I think strawberries will do."

"You sure? I have some weeping babies in the closet ready to go."

Marceline laughed. "I'm good."

* * *

Miles away from Marshall Lee's cave, a pink prince lay on his bed listlessly, head to the side to peer out the window, where fluffy white clouds chased each other across the skies.

He was worried for Fiona. The one real girl in his life, and she was off playing with fire. Literally. Prince Gumball's royal training and natural instinct told him he had to protect the little adventurer, but here he was, lying in pink plush while she was enjoying Flame Prince's company. He seemed like a good guy, but hello, he was made of fire. He'd burned Fiona before, what would stop him from doing it again?

On the other hand, last time Gumball tried to stop their date to the fire kingdom, not only was Fiona furious, but she went anyway. He didn't want his loyal fighter to hate him, but he also couldn't stand thinking off her sweet face twisted in pain from accidentally touching the burning man or incurring his fiery temper.

It was worrisome, to say in the least.

Gumball decided to run some experiments to keep his mind of the adventurous blond. On second thought, he opened the box of liquid pyrotechnics his niece sent him and read the note to himself.

_Uncle Gumball,_

_Lately there have been some…accidents with these. If you could find out a way to fireproof them while still finding a way to set them off…That'd be mathematical! I would but currently I'm working on some microbiology. Bacterium eating my people and all that…Thank you in advance!_

_Love, Bubblegum_

"They're fireworks. You don't fireproof. Fireworks." Gumball sighed and got to work on his special blueprint paper, redesigning and improving.

* * *

"If he's in a bad mood, will he send his little army after us?" Marceline asked nonchalantly, diving and floating on her back on their way to the Candy Kingdom. Marshall Lee had convinced her to do some harassing of the prince that lived there to get the prince in a better mood, even if the pink haired boy wouldn't admit it.

In Marshall Lee's mind, his twin was the best wing man for cooking up trouble in the world. Even if she'd never met the prince, she could find and press his buttons in a snap.

"Nah, he's a softy."

"Oh, here it is. Doesn't look much different from our Candy Kingdom."

"Bombs away!"

* * *

"Hold this here…Put this here…Clip…" Prince Gumball murmured to himself as he worked on the highest roof of the castle, perched precariously at the edge, legs crossed. Little drips of different colors spilled from the firework-shaped device in his hands.

"What's up, nerd?" Gumball dropped his pliers in surprise at the feminine voice behind him. He tensed and whirled around and relaxed as he saw a familiar skin color floating in his personal space.

"Marshall, stop taking cross-dressing so far. This time you're actually hot and it's weird," Gumball said before returning to his work.

"You cross-dress?"

"You left one of your outfits at my house last time. May as well put it to use."

"No shame."

"W-what?!" The prince nearly dropped his project off the roof, along with himself, as he turned again to see the vampire twins conversing in midair.

"So, Gumboy, you think my sister's hot?" Suddenly Gumball's friend was hovering in front of him, a wicked, sly smile across his face. He stuttered and glanced down to watch his niece's rocket take a long plunge into oblivion. Distantly, he hoped it didn't hit one of the soldiers stationed around this castles. More presently, he wished to have gone after it to avoid the awkward situation he'd landed himself in.

* * *

As Marshall Lee was busy pulling the prince's goggles away from his face to let them come back and slap him, Marceline pinned a grin on her lips. Inside, she was slightly flustered at being called hot. No one really ever called her that. Finn and Jake usually called her an ugly monster. It was…nice.

Stupid flattery.

She recomposed herself once again. She was the vampire queen, after all. Acting cruel and full of trickery was her specialty.

"I need to get Bubblegum's pyrotechnics!" Gumball squawked after the third goggle attack from Marshall, throwing his head over the side of the roof to peer down to see where the contraption had landed.

"The liquid pyrotechnics? That's what that was?" Marceline spoke up, peering with disinterest down the same direction Gumball was. "She hasn't needed those since the drought ended."

"But…" Gumball's face fell as he read a piece of paper in his hand. The sunlight hit the top of it so Marceline could see some of the girlish writing through the paper. It took a moment to read it, as it was backwards. _April 24, 3147_. It was June. Marceline tried to read more through the paper, but Gumball's slender fingers blocked the rest of the words. "I suppose we haven't really stayed in contact lately…"

"Why so plum, Bubblebutt?"

"Hey, that's what I call PB. You can't steal my nicknames!" exclaimed Marceline.

"You know Bonnibel?" Gumball asked in surprise, momentarily distracted from his depression.

"Yeah, Marcy lives in Ooo,too," Marshall Lee said before turning to his twin. "Doughboy here is PB's uncle. I'm so good at introductions," he added proudly. Marceline fondly punched him in the shoulder.

"Wait…are you the one she keeps writing about?"

"'The one'?"

"That interrupts all her experiments."

"Then, yes," Marceline chuckled.

* * *

Gumball blinked at the vampiress that floated before him, currently engaged in a who-can-shove-who-off-the-roof-first battle with her twin. She was winning.

Princess Bubblegum had often wrote of her one true friend back when they wrote to each other every day. Yes, Finn was a good protector, but was awkward and wasn't able to talk about girl stuff. A problem, she reminded him, was what was wrong with her own uncle as a friend as well. Gumball's sister had actually birthed his niece before he was born, as they had a great age difference. Bubblegum was a year older than her uncle.

"My friend" was all Bubblegum had to say in describing a story, as there was only one. She never named that friend, though. They'd apparently had a great relationship, even if her friend teased her and messed with her experiments. They could actually talk, and she knew her friend would never purposely hurt her. She was also friends with Finn, which was a bonus.

"Hey, let's make that frown turn upside-down. Would you go get his toy back, sister dearest?"

"Bite me," Marceline replied jokingly before flipping gracefully off the roof, out of sight.

"Gumball." The prince turned his attention from where Marceline had disappeared to meet Marshall Lee's suddenly serious red eyes, devoid of the humor that filled them only seconds ago. "That's my sister you're going cow eyed at."

"I-I wasn't going co—"

"Yes, you were, now listen close," Marshall hissed, cutting off his friend. "She's been through some serious Glob-forsaken stuff. You even think going after her, I'm going to rip your gumballs off."

"I—" Gumball began to squeak, but Marshall had already dived off of the roof.

"Let's go to Tree Trunk's and get some apples, yeah?" The prince heard Marshall faintly, a small sound of agreement from Marceline, and a "Give me that." Bubblegum's firework came flying over the roof and hit Gumball on the head before falling into his lap.

"...Ow"


	2. Liquid Pyrotechnics

**Author's Notes** | So I'm just having fun with this. Fluff fest, cheese fest, this-totally-wouldn't-happen-fest, I apologize but Adventure Time is just a silly show so silly fanfiction is in order! I promise I will get more serious in later chapters, however, whilst keeping some fun in. Excessive stupid nicknames. Because I can.

**Disclaimer**: I do not own Adventure Time with Finn and Jake. Some instances in the storyline may not match up with facts stated in the episodes of the series, these are my bad but probably on purpose to fit the plot better. I also do not own that one Ferris Bueller's Day Off reference...

* * *

The Vampire King peered into his recently inhabited guest bedroom, where his sister was dejectedly floating in circles, humming a broken tune.

"Still song blocked?"

"Yeah," she responded glumly.

"You're here on vacation! You didn't even bring your axe bass. Come on and enjoy all the wonders of Aaa."

"Fine," Marceline gave in, always the softie when it came to her minute younger brother. "What do you do for fun around here?"

"Messing with G—never mind. I know just the thing. Let me get some scissors."

* * *

"I haven't done this in ages!" Marceline whooped as they ran with the snarling canines all about them, the remaining half of her dark hair blowing out behind her like a lopsided cape. Her sibling flashed her a wicked grin from under his own uneven hair.

The wolves eventually tired from their midnight run, opting to pant and lie on a grassy hill, too exhausted to even howl and scare the young'uns of Aaa. The twins, however, were nowhere near done with their night.

"What we doin' next?!" exclaimed Marceline, in a wonderful mood.

"The night is young, dear Marceline. The question is 'what aren't we going to do?'"

"Well…what aren't we going to do?"

"Are you kidding me? I don't even know what we're going to do…"

"You're a goofball."

"Glob yeah I am! Let's go!" Marshall grabbed his sister's wrist and sped through the skies to Fiona and Cake's tree fort.

"What are we going to do here? Wow, this looks a lot like Finn and Jake's place," Marceline added as they snuck in through a window. BMO was nowhere in sight, and the rest of the fort looked empty.

"It was mine originally."

"I had Finn and Jake's first, too. Little twerps kick us out all over the world," she said before flopping onto the couch.

"Hey, get up lazy bones. We got work to do," Marshall said as he held up a massive array of super glue bottles in his bluish fingers.

For the next three hours in pitch black, the twins set to work gluing every single piece of furniture in the tree fort to the ceiling. They set to work meticulously, both being adept pranksters, mastered in the art of tomfoolery. No remote went unstuck, no glass of water unglued. They even glued the contents to the glass. The moon had begun its descent in the sky by the time they completed the task, both smiling gleefully at the job well done, gray faces lit malevolently in the dim light escaping into the house by window.

"Sun'll be up soon," remarked Marceline, peering through the glass at the setting moon.

"Better head home. Good job tonight, twin."

"Couldn't do it without you. I'm going home, you coming or what?"

"No," Marshall Lee said hesitantly, glancing upwards to the attic where they'd discovered a little shrine to the prince. The vampire had seemed glum after it, no matter how expertly he'd hid it. Marceline knew him too well. "I think I'll stay here a bit longer."

"Don't stay too long," Marceline advised him. She patted his shoulder sympathetically and floated through the window and into the open air.

* * *

Prince Gumball was once again perched precariously on his pinkish rooftop, turned purple in the dull darkness of night. The prince himself seemed less bright than normal, with his hair a violet and his skin lavender. The array of fireworks lined neatly along the gutter shone orange and red, all joined together by a white fuse leading to the devise in his dulled hands.

His safety goggles flashed as he struck a match, holding it to the fuse. Not even a spark. His lips curled upwards at the small victory, blowing the match out before he pressed the red button at the end of the white cord.

The pyrotechnics shot from their holsters in a colorful burst of light to explode across the near black velvet sky. Splashes of red, green, yellow, orange, purple rain dribbled down to patter harmlessly on the roofs speckled about the Candy Kingdom.

The prince beamed at his handiwork, propping a leg on his knee to lean on his own roof's incline. He crossed his arms behind his head and enjoyed the liquid rainbows still lingering in the air. A thin shower of blue and green mist wandered over on an air current to dust him in cool droplets.

"Did you do that?"

"Gah!" The man slipped in his surprise and flailed as he started a long plummet down towards the first floor's roof. That would hurt. He squeezed his eyes shut, when abruptly his arm felt like it was being ripped out of its socket. Slowly night sky filled his vision, then focused into twin, glowing red orbs. "M-Marceline?" Her slender fingers curled around his forearm, her hair fanning out from one side. A pale, pointed ear stood out starkly from the gray fuzz of her recently sheared undercut. Her lips were twisted into a fanged smile.

"Jumpy?"

"Just a little..." Suddenly Gumball realized he was suspended in midair. And so was the Vampire Queen. "H-hey I have a great idea...Let's get back on the roof!" The prince tried not to downturn his gaze, but sure enough the pink roofs far below soon multiplied and spun as Gumball felt increasingly sick at Marceline's slow swaying as the air wind gently pushed her levitating form about.

"Scared of heights, Gingerbread Man?"

"I'm scared of falling." That seemed to amuse the vampire, as she grinned wider and finally angled the both of them to land on the blessed pink shingles of the prince's roof. After he rejoiced in the wonders of solid ground, Gumball stiffened as he laid eyes on Marceline lit by the moon. "What happened to your hair?!"

"Marshmallow cut it to run with the wolves," she sang before floating on her back in the cool night air, flipping her remaining, ridiculously long locks.

"B-but why?" The prince continued to stare dumbly at her, mouth agape and uncomprehending of the loss of, well, one of her most beautiful features. The undercut looked crude on her, however it nearly fit her. Nearly. Gumball still preferred her full 'do. "Why in the world would Marshall Lee do that?" Gumball's eyes grew wide at the mention of his friend's name. "W-where is he now?" Purple eyes flashed nervously towards the horizon, scanning his sweet kingdom.

"Hanging in the tree fort. We glued everything to the ceiling." Her giggle somehow sounded adorable and malevolent at the same time, thought Gumball. "Ow!" There was a small sizzling sound as the rising sun's rays struck her cheek from beyond the overhang of the castle's tallest tower. "Glob!"

"M-Marceline..." And so the prince did the one thing that he usually did when Marshall was too stupid to avoid the light. He shucked off his lab coat and threw it over her head before grabbing hold of her waist and scooting the both of them around the spire of the roof opposite the sun. By that time the vampire queen had realized why it suddenly went blissfully dark and began thrashing about under the white fabric of his coat. Her head popped from under the collar, her arms thankfully encased in its overly large sleeves, hands disappearing in the excess of fabric needed to cover Gumball's lanky limbs.

"What the Glob, Gumballs?!" The furious vampire exclaimed, batting at him with his own lab coat's sleeves.

"Scared of the sun, Vamp?" The prince tried not to smile as he shielded his face and attempted to peer at the place where she'd been burned. "Where's the burn?" There was only smooth gray skin, slightly enflamed in Gumball assumed was outrage at being given a taste of her own medicine.

"I already healed," the queen spat, giving the prince another good few slaps before writhing out of his coat.

"Marshall doesn't heal that fast."

"I heal faster than him. Better upraising or minute older or something."

The prince couldn't hold back an excited, "Scientific!"

"I'm going to punch you."

"How are you going to get home now?"

The vampiress opened her mouth, then closed it in defeat. Her gaze turned towards her plain gray dress and red boots, not near enough to cover her for the trip home. "PB usually has a spare sunhat for me in her closet," she muttered thoughtfully, to Gumball's surprise.

"You stay until morning with her that often? I can't stand Marshall Lee for more than an hour. Maybe less."

"I've been told that I'm the good twin," Marceline chuckled absently, stealing a glance behind her to the ever-rising sun. "Speaking of which...he's probably home by now..."

"Don't you even dare try," Gumball said as sternly as he could, knowing full well what the vampire queen was about to do. His own friend had attempted on multiple occasions after staying too long to complete the perfect prank.

"How do you know what I was gonna try?"

"You were going to fly as fast as you could back to the cave and then hiss on the floor, complaining about life."

Marceline narrowed her eyes, but said nothing.

"Yeah. Come on, I think I have something that could help." Gumball led the seething queen down the ladder attached to the castle's candy wall, leading into his royal bedroom. He insisted on the highest room for the best view and perfect stargazing, along with access to the tallest roof. Marceline seemed out place in the dimly lit pink room spattered with candy knickknacks and the petty gadgets he kept lying about. She made herself at home nevertheless and sat on the overly cushy canopy bed in the center of the room.

"What is this thing made of? Cotton candy?" The queen said with a lopsided smile that matched her ebony hair, bouncing a few times. "It's like, ridiculously soft."

Gumball muttered something intelligible as he dug through his dark closet, unable to find the light switch in the still darkness. Luckily for Marceline, none of the three windows in his room faced the morning sun. However, it made rooting around for what he was looking for increasingly difficult.

"Ah, finally," the prince sighed as he withdrew the hoodie he wore when he had no princely duties. It was a bright raspberry and had been washed to the point that the text "2 Sweet 4 U" printed across the chest was unintelligible. The hood was overly large and would work well enough. "Here."

Marceline blinked, her lips pursing as she gazed at the proffered article in the prince's pink hands. "You actually wear un-prince stuff?"

"Well...yeah. I don't wear a collar and a puffy shirt to bed, or a crown when I'm on the roof. Doesn't Bonnibel wear un-princessly things?"

"Yeah, but I thought you were the proper one. PB is mathematical," Marceline said as she finally accepted Gumball's hoodie. "Thank you," she said, almost earnest before shrugging it on. It was too huge for her, and the hood drooped over her eyes to the point that the seam graced her nose.

"You should go on before the sun gets any higher."

"'Kay."

"Oh, and Marceline?"

"Yeah?" The vampiress halted, her shape boxed in by the window she was exiting in before the prince stopped her.

"Can you please not tell M-Marshall about you coming here?"

"Why not?" This time Marceline looked genuinely confused, her red eyes large under the shadow of the pink hoodie.

"Just please."

"I suppose. Thanks for the hoodie again!" And she was gone with a wave and a flash of pink.

"...Marshall's going to kill me."


End file.
